Full range light dimmer adaptor

ABSTRACT

A lamp dimmer adaptor is disclosed for insertion in a conventional lamp fixture to enable the illumination provided by an incandescent electric lamp to be controlled over a large range from dim to full intensity. The body of the adaptor has a socket for accepting the base of the electric lamp. Secured to the body is a hollow base formed by a metallic shell in which is housed a triac and all the other elements of the lamp dimmer circuitry with the exception of the variable resistor. The case of the triac is soldered to the shell to provide a thermal path for dissipation by the shell of heat generated in the triac. The body has a dependent collar which protrudes into the base and a recess in the collar receives the triac case whereby rotation of the base relative to the body is prevented. Above the base, the body has an external flat face which is substantially covered by a large hollow knob housing the variable resistor which controls the level of illumination.

United States Patent [191 Rodriguez [451 Dec. 25, 1973 FULL RANGE LIGHTDIMMER ADAPTOR [76] Inventor: Edward T. Rodriguez, 70 Meacham Rd.,Somerville, Mass.

[22] Filed: Sept. 13, 1972 [21] Appl. No.: 288,503

[52] US. Cl 315/58, 315/71, 315/272 [51] Int. Cl. HOlj 7/44 [58] Fieldof Search 315/58, 71, 291,

[5 6] References Cited UNITED STATES PATENTS 3,215,891 11/1965 Fritz etal. 315/71' X 3,256,466 6/1966 Trolio et al. 315/71 X 3,300,711' l/l967Duncan.. 315/71 X 3,372,302 3/1968 Fasola 315/71 X Primary Examiner-RoyLake Attorney-Louis Orenbuch 5 7] ABSTRACT A lamp dimmer adaptor isdisclosed for insertion in a conventional lamp fixture to enable theillumination provided by an incandescent electric lamp to be controlledover a large range from dim to full intensity. The body of the adaptorhas a socket for accepting the base of the electric lamp. Secured to thebody is a hollow base formed by a metallic shell in which is housed atriac and all the other elements of the lamp dimmer circuitry with theexception of the variable resistor.

The case of the triac is soldered to the shell to provide a thermal pathfor dissipation by the shell of heat generated in the triac. The bodyhas a dependent collar which protrudes into the base and a recess in thecollar receives the triac case whereby rotation of the base relative tothe body is prevented. Above the base, the body has an external flatface which is substantially covered by a large hollow knob housing thevariable resistor which controls the level of illumination.

2 Claims, 5 Drawing Figures 1 FULLv RANGE LIGHTDIMMER ADAPTOR Thisinvention relates to controls for electric lamps. More particularly, theinvention pertains to a socket insert for varying the intensity of alamp of the type having a filament heated to incandescence by anelectrical current.

It is common in domestic and industrial lighting application to controlthe intensity of illumination by the use of electronic light dimmers.Such dimmers employ a unilateralcontroller such as a silicon controlledrectifier or a bilateral controller such as a triac to regulate currentflow. Most electrical lamp sockets, however, are constructed with anon-off switch whereby the lamp is either at full intensity or is fullyextinguished. The principal objective of the invention is to provide alamp dimmer which can be inserted in the ordinary lamp socket to convertthe .on-off arrangement to an arrangement permitting the illuminationlevel to be con trolled over a large range.

The invention resides in a light dimmer adaptor containing within itselfan electronic circuit that permits the luminous intensity of anincandescent lamp to be controlled over a range from full intensity tovery dim or completely off. Although full range variable light dimmershave been employed for residential lighting, the use of such lightdimmershave usually been confined to installations, such as wallinstallations, which afford considerable space for housing theelectronic circuitry and where the electronic components are widelyremoved from the heat produced by the incan-' descent electric lampwhich the dimmer controls. The conventional full range light dimmeremploys a triac to regulate the current flow in the filament of thelamp. The triac is triggered by a triggering device controlled by aphase shift network. The phase shift network causes the triac to betriggered into conduction at a the remainder of the half cycle andreverts to its nonconductive state when the current drops to zero. Thetriac controls the flow of current to the filament of the lamp andthereby controls the luminous intensity of the incandescent filament.

To be commercially acceptable as an adaptor for use in the conventionalfloor and table lamp fixtures, the adaptor must contain within itselfall the electronic circuitry of a lamp dimmer and must be sufficientlysmall to permit the adaptor to be mounted in the socket of theconventional lamp fixture without increasing the height to the extentthat an electric light bulb cannot be mounted in the adaptor withoutremoving the lamp shade and its supporting stirrup. Further tofacilitate mounting in the conventional lamp fixture, the adaptor,

must be slender enough to rotate within the narrow aperture of thestirrup to permit the adaptor to be screwed into the socket of thefixture without requiring removal of the stirrup. The triac tends toproduce heat during the operation of the lamp dimmer and the electriclight bulb itself produces heat from the incandescent filament. The heatfrom these sources must be dissipated before the temperature rises to alevel that is damaging to the triac or the other components of thedimmer circuitry. The arrangement of the components of the adaptor toachieve the requisite heat transfer and the requisite small size is theessence of the invention.

The invention, both as to its arrangement and its manner of operation,can be better understood from the exposition which follows when it isconsidered in conjunction with the accompanying drawings in which:

FIG. I shows an embodiment of the invention disposed in a conventionallamp fixture;

FIG. 2 schematically depicts a lamp dimmer circuit suitable for use inthe invention;

FIG. 3 is an-exploded view of the preferred embodiment of the invention;

FIG. 4 is a view of the assembled preferred embodi ment; and

FIG. 5 is a view of the body of the adaptor with a portion of the wallbroken away.

A conventional lamp fixture is partially depicted in FIG. 1 to show thebody 1 of the fixture having affixed to it a conventional lamp socket 2containing an on-off switch controlled by a rotary knob 3. To providesupport for a lamp shade, a stirrup 4 is provided which is attached tothe body I and forms a frame around the socket 2. The stirrup has a wideaperture to accommodate the electric light bulb and has a narrower lowerportion which is closely spaced from the lamp socket. Atop the stirrupis a bracket 5 to which the frame 6 of the lamp shade is secured in theusual manner. The onoff switch of the conventional lamp socket permitsthe lamp 7 to be either at full intensity or fully extinguished. Toconvert the lamp fixture to a device permitting the illumination levelto be controlled over a range varying from full intensity to very dim, avariable lamp dimmer adaptor 8, constructed in accordance with theinvention, is situated in the lamp socket 2.

To permit the variable lamp dimmer adaptor 8 to be screwed into theconventional socket 2 without requiring removal of the stirrup 4, thecontour of the adaptor is such that it can pass through the narrowerportion of the stirrup. To maintain the height of the lamp within theaperture of the stirrup and to allow sufficient space to permit the lampto be unscrewed and removed, the height of the adaptor is kept as low aspossible consistent with the need to provide a receptacle for the baseof the light bulb.

FIG. 2 is a schematic diagram of the preferred circuitry employed in theinvention. The lamp 7 is in series with the main terminals Al, A2 oftriac 9 across the A.C. supply voltage impressed at terminals 10. Thegate of the triac is connected to a triggering device 1 I,

such as a diac. When the voltage across capacitor C2 triac gate. Thedischarge pulse triggers the triac into conduction for the remainder ofthe half cycle of the impressed A.C. The triac turns off during thebrief instant when the load current passes through zero.

The variable resistor R1 and capacitor C1 are connected in series tofonn. a charging circuit across the A.C. supply. Inasmuch as resistor R2and capacitor C2 are in series across capacitor C1, the configuration ofR1, R2, Cl, and C2 forms a double time constant circuit. The rate atwhich capacitors CI and C2 charge is determined by their capacitance,and the resistance in series with those capacitors. Because capacitorsC1, C2, and resistor R2 are fixed in value, the rate of charge iscontrolled by the setting of variable resistor R1. The double timeconstant circuit in conjunction with the triggering device effects phasecontrol whereby the triac connects the lamp to the AC. supply for acontrolled fraction of each cycle. Control is accomplished by causingthe triac to be triggered into conduction at a phase angle of the A.C.wave which is selected by the setting of the variable resistor. Once thetriac is triggered into conduction during a half cycle, it conducts forthe remainder of that half cycle. The circuit depicted in FIG. 2 affordsfull-wave phase control inasmuch as the triac can be triggered toconduct in either direction. To reduce hysteresis and the snap-oneffect, capacitor C1 is paralled by the series combination of capacitorC2 and resistor R2. The capacitor C2 acts to recharge capacitor C1 aftertriggering, thus reducing the snap-on effect. For a discussion of thesnap-on" effect see the SCR Manual, 4th edition, pp. 187-189, publishedby the General Electric Company.

From FIG. 2 it is evident that apart from the lamp 7 and the requisitewiring, only six components are employed in the circuit. Thosecomponents are so arranged in the adaptor that when the adaptor isscrewed into the socket of the lamp fixture, the adaptor is small enoughto rotate within the frame of the stirrup and provide sufficientclearance to permit an ordinary light bulb to be mounted in the adaptor.

In the operation of the lamp dimmer, the triac must dissipate heatwithout encountering a rise in temperature to a level that is unsafe forthat semiconductor device. The triac is therefore held in thermalcontact with a member of the adaptor which provides a large radiatingsurface for dissipating the heat transferred to it from the triac.

An exploded view of the preferred embodiment of the lamp dimmer adaptoris shown in FIG; 3, and an assembled view of that embodiment isillustrated in FIG. 4. The body of the adaptor 12 is molded of asynthetic material having the requisite electrical insulativeproperties. Preferably the body of the adaptor is molded from athermosetting plastic or from a thermoplastic material having a highmelting point. The adaptor body has an internal cylindrical opening 13in which is disposed a thimble 14 of copper which is threaded to receivethe base of a conventional light bulb. As shown in FIG. 5, a resilientspring 15 is secured at the bottom center of the floor of thecylindrical aperture to provide an electrical contact to the centerelectrode of the conventional light bulb. When a light bulb is insertedin the adaptor, electrical connection to the filament in the bulb isestablished through the thimble 14 and resilient spring 15.

The upper portion of the adaptor body 12 has a flat face 16 in which ashallow circular depression 17 has been formed. The depression serves tolocate the variable resistor R1 which has a flat circular body.Protruding from the variable resistor is a shaft 18 which can be turnedto change the resistance of, the device. The variable resistor R1 may bea commercially available miniature potentiometer. Preferably thevariable resistor is secured in the depression by an adhesive such as anepoxy resin. To permit electrical connections to be made to the variableresistor, the adaptor body 13 has two holes 19, 20 in its front facethrough which electrical conductors pass. A hollow knob 21 fits over thebody of the variable resistor and has a centralpost 22 which receivesthe shaft 18 of the variable resistor. The variable resistor isprincipally situated within the hollow knob 21 inasmuch as thedepression 17 in the adaptor body 13 is quite shallow. By housing thevariable resistor within the knob, the silhouette of the adaptor is keptto a narrow configuration which permits the adaptor to rotate within theframe of the stirrup 4 (FIG. 1) of the conventional lamp fixture. Thehollow knob preferably has a serrated edge to facilitate manualrotation. The knob is of an insulative material to isolate the user fromthe potential of the variable resistor. The knob completely covers thevariable resistor and is closely spaced from the front face 16 wherebythe variable resistor is encased between the body of the adaptor and theknob. The external diameter of the knob is equal to the width of thebody and the knob covers a large area of the flat front face 16. Foresthetic reasons the bottom portion of the flat front face is rounded toconform to the circular contour of the knob. Further conducing to aslender silhouette is the selection of a mechanically strong syntheticmaterial, such as a hard therrnosetting urea-formaldehyde resin, whichpermits the cylindrical wall of the adaptor body to be in the order ofone-sixteenth inch thick.

Below the flat face 16 of the body is a cylindrical collar 23 having asemi-circular recess 24 which receives the case of the triac 9, asdepicted in FIG. 5. The triac, shown in the exploded view of FIG. 3 hasits case soldered to the base 25 of the adaptor. The base 25 is threadedto fit with the threads of the conventional lamp socket. The base,preferably, is a brass shell having an insulated central electrode 26.The rim of the brass shell fits closely around the collar 23 when theadaptor is assembled. The rim of the brass shell is crimped oradhesively bonded to the collar 23 to secure the base to the body. Thereception of the triac 9 within the recess 24 of the collar acts toprevent turning of the base 25 relative to the body 12 of the adaptor.Preferably the case of the triac is bonded to the wall of the recess byan adhesive such as an epozy resin to further insure that the base doesnot separate from the body.

Within the brass shell of the base is situated an insulative disc 27'having electrical conductors formed on one surface in the manner of aprinted circuit board. Capacitors C1, C2, resistor R2 and the triggeringdevice 11 are mounted on the disc 27. In the assembled light dimmeradaptor, the triggering device 11 has one terminal connected to the gateof the triac. The triac is of the type having one of itsmain terminalselectrically connected to the case. By soldering the case to the brassshell of base 25, that main terminal of the triac is electrically tiedto the brass shell and the solder union provides a thermal bond throughwhich the triac transmits heat to the brass shell where the heat isdissipated by the relatively large surface area of the shell.

The triggering device 11 is a bi-directional device such as a diac whichbecomes conductive whenever its breakover voltage is exceeded in eithervoltage polarity. The typical diac has a breakdown voltage in the rangefrom 27 to 37 volts and is intended specifically for triggering diacs.Of course, neon bulbs can be employed as the triggering device but thebreakover voltage for such bulbs range from 50 to volts and areconsequently less desirable.

Although the circuit of FIG. 2 can be arranged to cause the triac to becut-off when the variable resistor is set for maximum resistance, it ispreferable to select the values of the circuit components so that thefilament of the lamp is faint but still visibly aglow at the maximumresistance of the variable resistor. By insuring that the triac is nevercompletely cut-off when the AC. supply voltage is present in thecircuit, problems arising from hysteresis and quick turn on arepartially averted. Further, the faintly glowing filament is a reminderto the user that the on-off switch of the conventional socket is set aton.

An adaptor constructed in accordance with the invention can be usedwithout requiring disassembly or alteration of the wiring of theconventional lamp fixture. The adaptor is relatively inexpensive becauseit requires few parts and is easily assembled.

Although the invention has been illustrated and described in the form ofa preferred embodiment, it is not intended that the invention be limitedto all the specific features of that embodiment. It is apparent to thoseskilled in the art of light dimmers, that some features 7 of thepreferred embodiment can be altered without departing from the essenceof the invention. It is therefore intended that the invention not beconfined to the specific embodiment here disclosed but rather that theinvention be delimited by the appended claims.

I claim:

1. A lamp dimmer adaptor for controlling the illumination provided by anelectric lamp of the type having an incandescent filament, the adaptorcomprising a body having a cylindrical socket adapted to accept the baseof the electric lamp, means in the socket for providing electricalconnections to the filament of the lamp, the body having an externalflat face, a variable resistor secured to the flat face, the variableresistor having a rotatable shaft for varying the resistance of theresistor, a hollow knob secured to the rotatable shaft and covering thevariable resistor, the variable resistor being housed principally withinthe hollow knob, the body having a dependent cylindrical collar belowthe cylindrical socket, a hollow conductive shell having its rimengaging the dependent cylindrical collar, the hollow conductive shellforming the base of the adaptor and being threaded to be received by aconventional lamp socket, a semiconductor device for regulating currentflow through the filament of the electric lamp, the semiconductor devicebeing disposed within the shell, the semiconductor device having itscase bonded to the shell whereby a thermal path is established to theshell for the dissipation of heat generated in the semiconductor device,the dependent cylindrical collar protruding into the shell and having arecess receiving the case of the semiconductor device, a capacitorwithin the shell, the capacitor being electrically connected to thevariable resistor to form a charging circuit therewith, and a triggeringdevice within the shell, the triggering device being controlled by thecharging circuit and being adapted to trigger the semiconductor deviceinto conduction.

.2. A lamp dimmer adaptor according to claim I, wherein the externalflat face of the body has a shallow depression therein in which aportion of the variable resistor is situated.

1. A lamp dimmer adaptor for controlling the illumination provided by anelectric lamp of the type having an incandescent filament, the adaptorcomprising a body having a cylindrical socket adapted to accept the baseof the electric lamp, means in the socket for providing electricalconnections to the filament of the lamp, the body having an externalflat face, a variable resistor secured to the flat face, the variableresistor having a rotatable shaft for varying the resistance of theresistor, a hollow knob secured to the rotatable shaft and covering thevariable resistor, the variable resistor being housed principally withinthe hollow knob, the body having a dependent cylindrical collar belowthe cylindrical socket, a hollow conductive shell having its rimengaging the dependent cylindrical collar, the hollow conductive shellforming the base of the adaptor and being threaded to be received by aconventional lamp socket, a semiconductor device for regulating currentflow through the filament of the electric lamp, the semiconductor devicebeing disposed within the shell, the semiconductor device having itscase bonded to the shell whereby a thermal path is established to theshell for the dissipation of heat generated in the semiconductor device,the dependent cylindrical collar protruding into the shell and having arecess receiving the case of the semiconductor device, a capacitorwithin the shell, the capacitor being electrically connected to thevariable resistor to form a charging circuit therewith, and a triggeringdevice within the shell, the triggering device being controlled by thecharging circuit and being adapted to trigger the semiconductor deviceinto conduction.
 2. A lamp dimmer adaptor according to claim 1, whereinthe external flat face of the body has a shallow depression therein inwhich a portion of the variable resistor is situated.